Study of Disorientation in Polycrystalline Hexaferrites and Application to the Design of a Ka-Band Planar Self-Biased Isolator

Self-biased circulators and isolators require pre-oriented hexaferrites with a high degree of orientation in order to ensure a magnetization perpendicular to the plane of the hexaferrite sample. In this paper, a strontium hexaferrite is selected for this application. Angular Remanence Measurements and XRD are performed in order to quantify the distribution of magnetization directions in this polycrystalline hexaferrite. The extracted distribution law was used to develop a model to predict the evolution of remanent magnetization as a function of shape factor. This model is then used to design a self-biased isolator in Ka-band. Insertion loss of 0.85 dB at 38 GHz was demonstrated with a quite good agreement with simulations.